I can't sudo cp on mounted volume?

[ironhak]

Hello, I'm trying to make a script that copies several files from mounted backup to my computer (both in home but also in root).
When I mount the backup I can't do say:

sudo cp  -R "/home/username/tmp_BORG/etc/"* /etc/

Because I would get permission denied, basically I can't do anything with sudo inside the mounted drive. How can I solve this?